Investment Calculator
Project how your investments could grow over time with an initial lump sum, regular monthly contributions, and compound growth.
Your expected return is treated as an effective annual return and converted internally to an equivalent monthly rate. Monthly contributions are assumed to be made at the end of each month, after that month’s growth has been applied.
These are illustrative assumptions only, not forecasts, predictions or guarantees of future performance. Your own investments could perform better or worse.
Growth vs No Investment Return
Year-by-Year Breakdown
Investment Calculator
Our Investment Calculator projects how a lump sum and regular monthly contributions could grow over time using compound growth. Choose an effective annual return, and see a full year-by-year breakdown of your contributions and growth, with an option to adjust the final figure for inflation. This tool is for illustration only and does not constitute financial advice.
How Compound Growth Works
Compound growth means your investment returns are reinvested and start earning returns of their own, alongside your original contributions. Over long periods, this compounding effect can account for a significant share of the final value, particularly when contributions are made consistently and reinvested for many years. The earlier you start and the longer you stay invested, the more time compounding has to work.
The percentage you enter is treated as an effective annual return: a 7% entry always means a 7% annual return, regardless of how often growth is notionally added. Internally, the calculator converts this into an equivalent monthly rate to apply growth consistently across each month of the term. Monthly contributions are assumed to be made at the end of each month, so that month’s growth is calculated on the existing balance first, and the contribution is added afterwards.
How to Use the Investment Calculator
- Enter your initial investment, the lump sum you are starting with (this can be £0 if you are only contributing monthly).
- Enter your monthly contribution, the amount you plan to add at the end of each month.
- Set your expected annual return, or use one of the preset assumptions as a rough illustrative guide.
- Choose your investment length in whole years, from 1 to 50.
- Optionally, add an annual contribution increase to model rising contributions over time, and tick adjust for inflation to see an estimated value in today’s money.
- Results update automatically, showing your projected future value, total contributions, growth earned, and a full year-by-year table.
What Return Rate Should I Use?
There is no single “correct” figure, since investment returns vary by asset type, time period and risk taken, and are never guaranteed. As a rough illustrative guide, UK cash savings accounts have historically returned around 3-5% a year, cautious multi-asset funds around 4-6%, and diversified stock market portfolios have averaged around 7-10% a year over long periods before charges and inflation, though with considerably more year-to-year volatility. These figures are not forecasts and past performance is not a reliable guide to future returns.
| Illustrative Assumption | Typical Range | Risk Level |
|---|---|---|
| Cash / savings | ~3-5% | Very low |
| Cautious multi-asset fund | ~4-6% | Low-medium |
| Balanced multi-asset fund | ~6-8% | Medium |
| Growth-focused fund | ~8-10% | Medium-high |
| Stocks / higher growth (illustrative) | ~9-11% | High |
How Contribution Timing Affects Your Projection
This calculator assumes monthly contributions are made at the end of each month: growth is applied to your existing balance first, then that month’s contribution is added on top. This is a deliberately conservative and consistent assumption, since a contribution made at the end of the month has one month less to grow than one made at the start. It is applied the same way throughout every calculation, so results stay comparable across different scenarios.
The Effect of Regular Contributions
Adding a fixed amount every month means you contribute consistently over time rather than investing everything at once. Consistent contributions, especially when increased over time in line with income growth, can meaningfully increase your final balance compared to a one-off lump sum of the same total value, because each contribution has a different amount of time left to grow.
Should I Adjust for Inflation?
Your future balance in pounds may look large, but inflation reduces what that money will actually buy by the time you reach it. Ticking the inflation adjustment option divides your projected future value by the effect of your chosen inflation rate compounded over the investment period, giving you an estimated value in today’s terms. The Bank of England’s long-term inflation target is 2%, though actual inflation varies year to year.
Frequently Asked Questions
Is this calculator financial advice?
No. This tool is for illustration purposes only, to help you explore how contributions, time and an assumed rate of return interact. It does not account for your personal circumstances, product charges, platform fees, or tax, and should not be relied on as a substitute for regulated financial advice.
How does the calculator convert my annual return into monthly growth?
There is no separate compounding-frequency setting. The percentage you enter is treated as an effective annual return, so a 7% entry always represents a 7% annual return regardless of how the growth is notionally applied. The calculator converts it internally to an equivalent monthly growth rate for the calculation. Monthly contributions are added at the end of each month, after that month’s growth has already been applied to the existing balance.
What does “growth multiple” mean?
The growth multiple shows how many times over your total contributions have grown by the end of the period. For example, a growth multiple of 2.5x means your final balance is two and a half times everything you paid in, combining your original contributions and the growth earned on them.
Does the calculator account for investment fees or tax?
No, figures shown are before any platform fees, fund charges, or tax on gains and income. These can meaningfully reduce your actual returns over time, so treat the results as a gross, before-cost estimate rather than a net figure.
What is the annual contribution increase for?
This optional field lets you model contributions rising each year, for example in line with a pay rise or planned increases in how much you save. It compounds your monthly contribution by the percentage you enter at the end of each full year of the projection.
Can I use this for a pension or ISA projection?
Yes, the underlying maths (a lump sum plus regular contributions growing at a chosen rate) applies to pensions, Stocks and Shares ISAs, or general investment accounts alike. For pension-specific figures including employer contributions and tax relief, see the Pension Calculator. For a tax-free wrapper aimed at first homes or retirement with a government bonus, see the Lifetime ISA Calculator.
Why does the “no growth” comparison matter?
The Growth vs No Investment Return table shows what you would have if the same money simply sat with no return at all, so you can see how much of your final balance comes purely from investment growth rather than from what you paid in yourself.